In an electroluminescence (EL) device, a light emitting layer is formed on a transparent substrate so as to be interposed between an anode and a cathode. When a voltage is applied between the electrodes, light is emitted by exciters generated by recombination of holes and electrons injected as carriers to the light emitting layer. EL devices are generally classified into organic EL devices in which an organic substance is used as a fluorescent substance of a light emitting layer, and inorganic EL devices in which an inorganic substance is used as a fluorescent substance of a light emitting layer. In particular, organic EL devices are capable of emitting light of high luminance with a low voltage, and various colors of emitted light are obtained therefrom depending on the types of fluorescent substances. In addition, it is easy to manufacture organic EL devices as planar light emitting panels, and thus organic EL devices are used as various display devices and backlights. Furthermore, in recent years, organic EL devices designed for high luminance have been realized, and attention has been paid to use of these organic EL devices for lighting apparatuses.
FIG. 4 shows a cross-sectional configuration of a common organic EL device. In an organic EL device 101, a translucent anode layer 104 is located on a translucent substrate 105, and an organic layer 103 which is made up of a hole injection layer 133, a hole transport layer 132, and a light emitting layer 131 is located on the anode layer 104. A light-reflective cathode layer 102 is located on the organic layer 103. When a voltage is applied between the anode layer 104 and the cathode layer 102, light which is emitted by the organic layer 103 passes through the anode layer 104 and the substrate 105 and then is taken out. In general, a metal material such as aluminum (Al), silver (Ag), or the like, which has a high light reflectivity and electrical conductivity, is used for the cathode layer 102.
However, it is known that in the metal material having the high electrical conductivity, plasmons, which are collective oscillations of free electrons in the metal behaving as pseudo particles, occur. That is to say, it is known that when light of a predetermined wavelength enters a surface of a metal material, a wave of electron density pattern, namely, a surface plasmon is excited, and the surface plasmon propagates through a surface of the metal and is inactivated (refer to 10th Symposium on Organic EL Regular Meeting Proceeding, S9-2, for example). Thus, in the organic EL device 101 shown in FIG. 4, part of light which enters the cathode layer 102 in light emitted by the light emitting layer 131 (indicated by a star) propagates through a surface of the cathode layer 102 and is inactivated (indicated by arrows), so that it is not taken out as effective light, and thus light extraction efficiency is often reduced.
In order to suppress a light loss caused by the surface plasmon, there is a thought that a nano-order unevenness is provided on a substrate, and an organic layer, which includes an anode layer and a light emitting layer, and a cathode layer which is formed of a metal are laminated on the unevenness to form a corrugated structure at each interface (for example, refer to Japanese Laid-Open Patent Publication No. 2009-9861: Patent Document 1). According to the above configuration, the surface plasmon occurred on the surface of the metal changes to a propagation light by the uneven corrugated structure, so that the light loss caused by the surface plasmon can be suppressed.
However, in the uneven corrugated structure described in the above patent document 1, since the unevenness is formed at the interfaces of all the layers, a film thickness becomes ununiformed and a short circuit occurs easily, so that there is a possibility that reliability of a device in which the above organic EL device is incorporated is reduced.